1. Field of the Invention
The present invention relates to a surface emitting device that increases the amount of light perpendicularly emitted therefrom and thus has uniform distribution of light over an entire light exit surface.
2. Description of the Related Art
Surface emitting devices such as backlight units are used in liquid crystal displays (LCDs), which are non-emissive displays and thus use external light to produce an image.
Surface emitting devices are classified into direct light type devices and edge light type devices. Direct light type devices are configured such that a plurality of light sources disposed beneath an LCD panel directly emit light onto the LCD panel. Edge light type devices are configured such that a light source is located on a sidewall of a light guide plate (LGP). Since the light sources can be freely and effectively located over a wide area, the direct light type devices are generally used in relatively large displays. Since the light source is located on the sidewall of the LGP, the edge light type devices are generally used in relatively slim and small displays, such as small and medium-sized displays used for monitors or mobile phones.
FIG. 1 is a perspective view of a conventional edge light type surface emitting device. Referring to FIG. 1, the conventional edge light type surface emitting device includes light sources 10 and an LGP 12. The LGP 12 has a side surface, acting as a light incident surface on which light emitted by the light source 10 is incident, and a top surface, acting as a light exit surface from which the incident light is emitted. The LGP 12 guides incident light thereon inside the LGP 12 by total reflection and emits the same through the top surface thereof. Holographic patterns 14 are formed on the top surface of the LGP 12. The holographic patterns 14 diffract light such that the light is emitted at an angle substantially perpendicular to the top surface, i.e., the light exit surface.
Light emitted by the conventional edge light type surface emitting device should have uniform brightness over the entire light exit surface, but there are some problems in obtaining such uniform brightness.
The uniformity of light exiting the LGP 12 on which the holographic patterns 14 are formed varies with the angle of light entering the holographic patterns 14. Accordingly, to achieve uniform brightness, the angle of light exiting the LGP 12 should be controlled properly.
Also, in the case of the conventional surface emitting device constructed as described above, the amount of light decreases at distances farther away from the light sources 10. Furthermore, hot spots are formed in a light incident portion near the light sources 10 and regions around the hot spots are darker.
Many attempts have been made to solve these problems by making less perceptible the holographic patterns 14 of the LGP 12 around the light incident portion, inserting a separate pattern to scatter light from the light incident portion toward side surfaces, or separately designing and manufacturing the light incident portion to increase the divergence angle of the light sources 10.